System and method for reducing memory use associated with the graphical representation of a list control

ABSTRACT

A system and method are disclosed whereby a list-based control (e.g., a Listbox or Choice control) in a graphical user interface may share a single copy of a list with the peer component of the control in the application program interface (API) used to display the control. This overcomes a problem in legacy Java applications, based on the abstract windowing toolkit API, wherein the peer component creates a copy of the list when the corresponding list-based control is displayed. In contrast, peer components within the Swing API reference the original version of the list associated with the control, avoiding this redundancy. According to the system and method disclosed herein, an enhanced version of Swing can be used with legacy application programs, allowing them to benefit from this feature of Swing. No modification of the legacy code is necessary. This extension to Swing is referred to herein as AWTSwing.

RELATED APPLICATIONS

[0001] This application is related to the following co-pending U.S.Patent Applications, filed on even date herewith: “System and Method forEncapsulating Software Components in an Application Program InterfaceUsing a Proxy Object,” “System and Method for Fast Drawing of TextFields and Labels in a Java Swing Application Program Interface,”“Combining the Functionality of Multiple Text Controls in a GraphicalUser Interface,” “Inheritance of Background Color in a ContainmentHierarchy of Objects in a Graphical User Interface,” “Dynamic Bufferingof Graphic Images by a Platform Independent Application ProgramInterface,” “System and Method for Implementing a Graphical UserInterface Across Dissimilar Platforms Yet Retaining Similar Look andFeel,” “System and Method for Introducing Enhanced Features into a JavaSwing Application Program Interface,” and “Application Program Interfacethat can Maintain Similar Look and Feel of a Displayed Image Regardlessof Whether the Interface is Platform Dependent or Platform Independent,”all by Scott J. Broussard.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] This invention relates to computer software, and moreparticularly to software for a graphical user interface used to allow alist to be presented upon a computer display, and control thereof. Thesoftware allows the list to be displayed and controlled from a singlefile created within local memory, without using duplicative filescreated by the application program and the operating system.

[0004] 2. Description of the Related Art

[0005] The continuing proliferation of faster and more powerfulcomputers has been accompanied by an increase in the use of graphicaluser interfaces. A graphical user interface (or, GUI) offers manyadvantages over traditional text-based interfaces. A graphical interfacemay allow multiple application programs to present outputsimultaneously, each in a distinct window. Thus, it is not necessary tohalt one application in order to interact with another. Instead ofentering text-based commands and parameters, the user selects icons witha pointing device, such as a mouse. This is faster, easier and lesserror prone than making these selections using the keyboard.

[0006] GUIs are based on the development of object-oriented programminglanguage. Object-oriented programming languages are based on lines ofcode or “objects” that, when executed, produce an image upon a computerdisplay. Modern object-oriented programming languages can often bewritten and developed in a relatively short period of time. For example,an application written in programming language A may run 30% faster on agiven computer than the same application written in programming languageB. On first impression, it would seem that language A is superior to B.However, the programmers using language A may need two months tocomplete the application, while language B can be finished in a week. Inmany cases, the additional speed gained by using language A isunimportant. For example, if the application spent most of its timewaiting on user input, the 30% speed improvement would not benoticeable. On the other hand, the length of time required to write theprogram is almost always important, since it reflects development cost.This has led to introduction of modern object-oriented programminglanguages, such as C++ and Java. Often accompanying the new languagesare rapid application development (or, RAD) environments, whichtypically combine compilers, editors, code debuggers, and other featuresin a programmer's “toolkit” to accelerate application development.

[0007] Object-oriented programming languages represent a new paradigmfor software design. Computer programs have traditionally beenstructured as a sequence of operations, which implements an algorithm orprocedure. However, the traditional procedural model suffers fromseveral weaknesses that limit its usefulness for modern software design.In the early days of computers, software programs were of limited sizeand complexity. Since these programs were typically written by a smallgroup of programmers (often, one individual), it was comparatively easyto ensure that consistent software standards were observed, and issuessuch as portability and reuse of code were given little consideration.Today's software programs are often huge composites of complex,interacting code developed by disparate teams of programmers. Modemsoftware development requires coordinating the efforts of manyindividuals to develop a unified, consistent body of software. In theselarger, more complex software projects the shortcomings of proceduralprogramming languages become apparent. One area of difficulty thatemerges is in maintaining consistent interfaces between the componentsof a large software program. Software routines interact with each otheror exchange data via an interface—i.e., a set of statements, functions,options, etc. for expressing program instructions and data provided byone program segment for use by a another program segment. For example, aprinter driver may be called by various other routines in a program toproduce hardcopy output.

[0008] As noted herein, a software component is any sequence ofexecutable code. The code can be executed from an operating system whichconfigures the computer or microprocessor. When dealing with GUIs,software component can be a sequence of code lines that define an imagepresented on a computer display. Thus, a sequence of code, deemed asoftware component, can contain instructions for generating an image.Such a software component can be alternatively known as an “object.” Forexample, the GUI software component is alternatively known as an object,and the object can provide an image upon the display when executed by aprocessor. In order to operate effectively, it is important that theinterface between software components be fully defined and be adhered toscrupulously. For highly complex and extensive programs, this can entaila great deal of effort and can have considerable impact on softwaredevelopment time.

[0009] Code reusability is another important factor in modem softwaredevelopment. Time-to-market considerations dictate that reuse ofexisting code is preferable to writing new code. For example, aprogrammer developing software to perform spectral analysis may requirea program to compute the Fourier transform. It may take him two weeks towrite and debug such a program, but just two days to modify apre-existing program for his needs. Since it is generally more efficientto reuse code than to recreate it, there has been an increasing emphasison modularity in software design. Modular code is self-contained and haswell defined input and output parameters, allowing it to be easilycombined with or integrated into other code.

[0010] The object-oriented paradigm has arisen to enable fasterdevelopment of complex software programs. It encourages the use ofconsistent interfaces between program modules, and is conducive to thecreation of reusable, modular code. These features are highlyadvantageous in the development of large, intricate software programs,requiring the coordinated effort of several programmers.

[0011] A departure from traditional programming languages, theobject-oriented paradigm is based on objects, rather than procedures.The fundamental entities in an object-oriented programming (“OOP”)language are classes created by the programmer, which possess propertiesappropriate for their intended purpose. Once a class has been defined,one or more objects can be created as instances of the class. Individualobjects possess all the attributes of the class they represent. Forexample, a software component (e.g., a program for a GUI) might containobjects such as windows, menus, buttons, etc. having properties such ascolor, size, location on screen, etc. In addition to their properties,objects also have methods. Methods are actions supported by the object,by means of which they interact with other objects or respond toexternal events. A major difference between OOP languages andtraditional procedural program languages is that the methods andproperties of an object are encapsulated. In object-orientedprogramming, encapsulation refers to the inclusion within an object ofall the resources needed for the object to function—basically, themethod and the properties. Other objects adhere to these interfaces touse the object without having to be concerned with how the objectaccomplishes it. This makes it easier to ensure that objects interfacewith one another in a consistent manner, and also protects the internaldata of the object from unintentional corruption by other programcomponents. By virtue of encapsulation, an object can be thought of as aself-contained atom. When an object is created, certain of itsproperties and methods are defined as “public,” and the remaining onesas “private.” Only the public properties and methods are accessible toother objects; the private properties and methods are protected. Forexample, the properties and methods of a sequence of code (i.e., anobject) of a GUI software component which defines the color of a windowand the menu layout can be accessible by another object which definesanother window, menu, and scroll bar layout so that the first object canbe dependent on the second object for producing a sequence of windows,each having its own property and method dependent on each other.

[0012] Encapsulation also benefits code reuse by simplifying the mannerin which an object is accessed. For example, a programmer can reuse apreviously created object having a method that performs a Fouriertransform. In an object-oriented scenario, he simply includes the objectdefinition in his program, and references its method when needed. It isgenerally not necessary to closely examine or modify the code within theobject, since the object method completely defines the interface. Afeature of object-oriented programming languages that further benefitscode reusability is inheritance. The concept of inheritance is thatcertain software components, or objects, can inherit the properties andmethods of a parent software component, or object. Thus, objects of codecan be developed as modular building-blocks, with subsequent objectsbeing children of parent objects. For example, a parent object whenexecuted by a processor may produce an image indicative of an entirewindow and when executing a child object, the child object produces asub-window, or template, within the parent object-executed window, orimage. Importantly, the parent object can define a class, and the childobject can inherit the class (properties and methods) of the parentobject. In addition, the child object can also take on further methodsand properties unique to the child object class. For example, a “jet”class can be defined as a child of an existing “airplane” class, withadded properties, such as “turbine velocity.” Once the subclass exists,the programmer is free to create new objects with jet-like properties.

[0013] Some objects have a graphical representation. For example, it iscommon to include buttons, checkboxes, and other similar “controls” in aGUI belonging to an application program. Images associated with theseobjects are displayed on a computer screen to allow the user to interactwith the application. Among the methods of such objects are displaymethods (e.g., “paintIcon”, which can be invoked to make the objectappear on the computer screen. When a displayable object (i.e., objectbeing a sequence of code) is created by an application program, its sizeand location with respect to a “layout” must typically be declared. Alayout is a region of the screen allocated for the display of a givenset of controls, and within which the arrangement and orientation of thecontrols are established. To permit a user to interact with the GUI,displayable controls typically include methods enabling them to respondto external events, such as mouse button clicks. The object code that isthe recipient of a user event (e.g., a pointer device placed over abutton displayed on a computer display) is referred to as the targetobject. Thus, a target object can receive method-type code imparted toit when a user interacts with the GUI.

[0014] Java is a modern OOP language, designed with an emphasis onportability. As used herein, the term “platform” refers to a specificcombination of hardware and operating system. More specifically, aplatform consists of an operating system, the computer system'scoordinating program, which in turn is built on the instruction set fora processor or microprocessor, the hardware that performs logicoperations and manages data movement in the computer. A software programis said to be “portable” across various platforms if the program can runwithout modification on any of those platforms. This “write once—runanywhere” principle is the underlying philosophy behind OOP languagessuch as Java.

[0015] The portability of Java depends on the presence of a Java virtualmachine (JVM) in the target computer (i.e., the computer on which theJava application is to execute). A JVM “translates” the generic Javacode into instructions specific to the target machine (i.e., “native”code) at runtime. Therefore, the same Java program can run withoutmodification on any computer for which a JVM exists.

[0016] Since its introduction, Java has found use in many areas,including GUI development, where the portability of Java code is highlyadvantageous. As used herein, the “look and feel” of a GUI refers tosuch things as the appearance, color and behavior of Buttons,TextFields, Listboxes, menus, etc. and their mouse, keyboard handlingand behavior. Look and feel is the generic way in which to describe theappearance of an image on a computer display to that of another image ona computer display. If the window, icons contained within the window,the control menu, the general layout of that window, and the colors ofthe various features shown on that window are similar to that of anotherwindow image, then the two images are said to have essentially the samelook and feel.

[0017] Often, a software program is intended to run on various machines,or under various operating systems, while maintaining a consistent lookand feel. If the GUI is written in Java, a great deal of the code can becommon across platforms, since Java is portable. This shortensdevelopment time, since the developer only has to write one version ofthe GUI code to be ported to all of the desired target machines oroperating systems. It also improves maintainability of the code. Whenbug fixes or feature upgrades are necessary, they are confined to oneversion of the code, rather than several machine/system-specificversions.

[0018] Unfortunately, the portability of Java does not guarantee acompletely consistent, platform-independent look and feel for aJava-based GUI. This is because the GUI still derives some of the lookand feel of the platform through its reliance on an application programinterface (“API”). An API is an interface used by an application programto access operating system services. Therefore, API is an interfacebetween the application program and the operating system, or platform.The UIManager is a constituent of the API that contains the look andfeel settings of the GUI. By making calls to the API, an applicationprogram can invoke the resources of the operating system, for example,to write to the computer screen or detect the position of the mousecursor, or to request the current look and feel settings. Traditionally,Java applications utilize an API known as the abstract windowing toolkit(“AWT”). Using the AWT, multiple platform-specific implementations ofeach GUI component, known as component Peers, can be created. ComponentPeers or software component Peers are object lines of code that containone or more such lines unique to the operating system in which thecomponent software Peer is intended to interface. When executed, thecomponent Peer will produce an image dependent on the operating systemsince the program interface of an AWT is platform dependent. Due to theplatform-dependence of the interface toolkit or AWT, different operatingsystems will have different AWT implementations. As a result of thesedissimilarities, the appearance of controls (i.e., buttons, lists,checkboxes, etc.), created by a Java-based GUI will vary when the GUI isported to different platforms.

[0019] The platform-dependence of the AWT also increases the difficultyof enhancing and maintaining Java GUI application code. In order to adda new feature to the GUI, for example, it is necessary to modifydissimilar code in the AWT for each supported platform. Moreover, it maybe extremely difficult to obtain consistent behavior from the addedfeature, because of code differences in the platform-specific AWTs.

[0020] Text rendering is another consideration in the development of aplatform-neutral GUI. Various platforms employ diverse methods ofdrawing text, some of which are more efficient or yield better qualitythan others. The native methods used in many AWTs can use only one fontat a time, and do not support font searching to locate the glyphs(graphic symbols that provide the appearance or form for a character)required for accurate text rendering. Because of this, the consistencyof the look and feel may be lost when the GUI is ported from a systemwith good text quality to one with poor text quality.

[0021] Furthermore, many operating systems do not use unicoderepresentations for text, making them susceptible to conversion errorsor limited character set coverage. Unicode is a new standard forassociating binary codes with text or script characters. Officiallycalled the unicode Worldwide Character Standard, it is a system for theinterchange, processing, and display of written text in all the majorlanguages of the modem world. Currently, the unicode standard contains34,168 distinct coded characters derived from 24 supported languagescripts, covering the principal written languages of the world. Unicodesupport is important for a universal, platform-independent GUTI.However, dependence on the platform-specific AWT presents an obstacle tothe use of unicode in a Java-based GUI.

SUMMARY OF THE INVENTION

[0022] The problems outlined above are in large part solved by a system,method, and computer-readable media for producing a platform-independentapplication GUI program interface, API. The API receives an applicationprogram and produces a software component (object). The object is GUIcode that, when executed by a processor, produces an image on a computerdisplay. The improved API can either have its own native code or, incontrast, can derive its code from an ancestor software component. Thus,in the latter example, the API has no native code, but borrows or“inherits” its code from another software component.

[0023] If the API has its own native code, the API is said to be aheavyweight software component. The AWT uses a software component calleda Peer, which is necessary in order to interface with the particularoperating system, or platform, in which it is coupled.

[0024] In instances where the API is a lightweight software component,the API inherits its code from other components. There may be multiplesoftware components from which the API inherits its properties andmethods. Those ancestor components are often referred to as “Swing” APIsoftware components and available to be borrowed from.

[0025] By using the resources of Swing software components in lieu ofcorresponding AWT components, a more portable, platform-neutral API canbe created. The API can, therefore, ideally produce a software component(object) as platform independent, and which generates an image which hasthe same look and feel independent of the operating system used. Legacyapplications using the AWT can be updated to use equivalent Swingcomponent Peers. However, several complications prevent Swing from beingable to completely or directly replace the AWT.

[0026] Swing components cannot directly replace AWT Peers, since the AWTcontrols created by a legacy application are already present in alayout, and AWT controls generally cannot act as containers for othercontrols. Swing software components cannot replace the heavyweight AWTPeers because the Swing components are designed for a different role orpurpose within the system, which typically cannot be modified. In otherwords, there are limitations inherent in the design of the Java JVM thatare unalterable, and therefore this invention must work within thoseconstraints.

[0027] Furthermore, because Swing buffers its output, when several Swingcomponents are contained within each other, performance can suffer(relative to an equivalent AWT implementation).

[0028] Also, Swing does not allow the association of look and feelcharacteristics with a particular thread. This makes it impossible foran application to have its own unique look and feel, while the operatingsystem under which the application is running maintains the global lookand feel of the platform.

[0029] In addition, the architecture of the JTextField andJPasswordField components in Swing is different from that of theTextField AWT component. Unless modified, these Swing components may notfunction properly when used by the legacy application. Moreover, SwingTextField and Label component Peers often exhibit poorer performancethan their AWT counterparts.

[0030] A further consideration when evaluating Swing as an API for aportable GUI is the limited functionality of Swing. Swing lacks some ofthe functionality available in the better native GUIs (such asWindows®). For example, the Windows operating system provides thecapability for application programs using text components to popup menus(e.g., for help-related functions) with undo/redo and editing support.This capability is absent from Swing text components, as well as thelegacy AWT. Therefore, there is a need for a platform-independentreplacement for the AWT that overcomes the above-mentioned limitationsof Swing.

[0031] In view of these, and other considerations, it would be desirableto have some means of replacing the heavyweight AWT Peer classes withlightweight Peers (such as those in Swing), while avoiding the problemsand limitations described above.

[0032] The API having both Swing-type features and AWT-type features isalternatively called “AWTSwing,” and can be used to provide improvedfunctionality and a more consistent look and feel for Java applicationprograms. AWTSwing replaces the heavyweight Peer classes in the AWT withlightweight Peer classes while preserving the same interface. Thisallows legacy applications, which previously relied upon the graphicsresources of the AWT, to run without modification. AWTSwing alsoaugments the functionality of Swing, so that new applications can deploya modern full-featured graphical interface. Because AWTSwing uses nonative code for the windowing controls, it is truly portable. Therefore,the GUI for a Java application based on AWTSwing will have a consistentlook and feel regardless of which operating system it is ported.

[0033] According to one embodiment, a display system is contemplated.The display system is one applicable to a computer system, and moreparticularly includes a display (i.e., computer monitor), a graphicaluser interface, and a processor. The processor can be adapted to operatefrom an operating system, such as a Windows-based operating system. Theprocessor is coupled to not only the operating system, but also asoftware component, during run-time of an application program. Thus, theapplication program initiates a software component. Alternatively, thesoftware component can be considered as a sequence of code of theapplication program, such code being that which produces an imageaccessible by a user via the graphical user interface. When executingthe software component by the processor, the processor generates a firstimage upon the display independent of code within the operating systemduring a first time. During a second time, the executed softwarecomponent emulates code that generates a second image upon the displaydependent of code within the operating system. Thus, the softwarecomponent is contained within an API as either having its own nativecode dependent on the operating system, or simply having a templatewhich can borrow from a parent software component contained within aplurality of Swing components. In the former instance, the softwarecomponent has code unique to the operating system, but in the latterinstance, the software component has code entirely separate from theoperating system. More particularly, the software component in thelatter instance, would borrow code from an ancestor, Swing componentcontained within a library of Swing components separate and apart from,and not dependent in any way upon, the operating system or platform onwhich the processor will run. Advantageously, the software componentcontains an object which will have the same look and feel when executedby the processor and displayed on the display device, regardless of theoperating system. Thus, the buttons, list boxes, scroll bars, icons,colors, shading, etc. of the image will look substantially the sameregardless of whether the API is using a platform specific API (AWT-typeAPI) or a platform independent API (Java Swing-type API). Furthermore,the software component can utilize an AWT-type API or a Swing-type APIeither in combination, or separately. For example, it is possible fortwo sub-components to use two different APIs, or for all sub-componentsto use a single API at one time and a different API at another time.

[0034] According to another embodiment, a method is provided. The methodis one which displays an image on a computer display. The computer canrun an application program that includes an API dependent on theoperating system of the computer to cause a first image to be displayedusing the first interface. Thereafter, the computer can run anapplication program with a second interface that is substantiallyindependent of the operating system, yet emulates the behavior of atleast a part of the first interface. The application program can then bere-run to re-display the second image having substantially the same lookand feel of the first image.

[0035] According to yet another embodiment, a computer readable storagedevice is presented. The storage device includes computer-executablecode, such as an operating system and an application program. Theapplication program can execute code of a software component during afirst time and during a second time. During the first time, the code isexecuted by generating a first image independent of executing codewithin the operating system. During the second time, code of thesoftware component is executed to generate a second image dependent onexecuting code within the operating system, where the first image canoverwrite an image upon a display screen previous to the first image.However, the first image cannot overwrite the second image upon thedisplay screen during the first time. In other words, the softwarecomponent cannot execute an AWT-type API, and map the software componentoutcome thereof to a Swing-type API. Instead, either the AWT-type API isexecuted or the Swing-type API is executed, at two dissimilar times, notin series with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Other objects and advantages of the invention will becomeapparent upon reading the following detailed description and uponreference to the accompanying drawings in which:

[0037]FIG. 1 illustrates a computer system capable of supporting agraphical use interface with a consistent look and feel across diverseoperating systems;

[0038]FIG. 2 illustrates in more detail the interface between anoperating system (OS) and an application program;

[0039]FIG. 3 illustrates how controls in a user interface aregraphically represented with the AWT;

[0040]FIG. 4 illustrates how controls in a user interface aregraphically represented with Swing;

[0041]FIG. 5 shows the relationship between the elements of the JavaFoundation Classes;

[0042]FIGS. 6a and 6 b illustrate the z-order of graphical controlswithin a container;

[0043]FIG. 7 illustrates the flow of event notifications and methodcalls in an AWT-based application program;

[0044]FIG. 8 illustrates how controls in a user interface aregraphically represented with a lightweight replacement for the AWT API,embodying the system and method disclosed herein and referred to hereinas AWTSwing;

[0045]FIG. 9 represents the alternate use of application programinterfaces containing heavyweight and lightweight software components;

[0046]FIG. 10 shows the flow of event notifications and method calls inan AWTSwing-based application program;

[0047]FIG. 11 illustrates the creation, under the AWT API, of redundantmemory arrays to store the elements of a list-type control;

[0048]FIG. 12 illustrates the use, by AWTSwing, of a single memory arrayto store the elements of a list-type control;

[0049]FIG. 13 represents the logic within a fast text drawing methodwithin AWTSwing;

[0050]FIG. 14 illustrates buffering of image data, normally performed bythe Swing API;

[0051]FIG. 15 depicts the method used by AWTSwing to automaticallyenable or disable buffering of image data, based on the display hardwareconfiguration;

[0052]FIG. 16 illustrates the operation of an enhanced UIManager, whichsupports thread-relative look and feel settings;

[0053]FIG. 17 represents the alternation of two Swing controls toemulate the functionality of a legacy TextField control;

[0054]FIG. 18 shows a flowchart representation of the logic foralternating the two Swing controls; and

[0055]FIG. 19 represents a scheme for background color inheritanceemployed by AWTSwing.

[0056] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription thereto are not intended to limit the invention to theparticular form disclosed, but on the contrary, the intention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0057] The need for rapid development of software programs has led tothe introduction of modern object-oriented programming languages, suchas C++. Among current OOP languages, Java is regarded as a “writeonce—run anywhere” language. This is because, unlike programs written intraditional languages, Java programs can be run without modification onvarious different computers or under different operating systems.However, a Java application may not be completely portable in terms ofthe look and feel of its graphical interface. This can occur if theapplication makes use of the windowing resources of theplatform-specific AWT. The numerous operating system-specific versionsof the AWT are mutually inconsistent in regard to the graphic featuressupported and the manner in which those features are implemented.

[0058]FIG. 1 illustrates a computer 10. Computer 10 includes amicroprocessor 12 which operates from any given instruction set, such asa reduced instruction set or X86 instruction set. Coupled to processor12 is a pointing device 14, such as a mouse or keyboard arrow indicator.A computer display 16 is also provided for displaying images produced bythe processor, when executing an application program. A memory 18 can becoupled to processor 12. Contained within memory 18 may be a Javavirtual machine (JVM), a graphical user interface (GUI), an applicationprogramming interface (API), operating system (OS) program, and anapplication program (AP).

[0059] The Java JVM contains a toolkit, which is a translator. Thetoolkit can be written in Java for execution by the JVM via the API.Translator toolkit 20 is portable across multiple OS platforms, and,translates or adapts standard platform-independent java code to nativejava code. The toolkit defines the platform specific implementationobjects that comprise the GUI for use by a software application.

[0060] Translator toolkit 20, therefore, takes the application programpresented to the API and translates GUI information to a form usable bythe operating system. Accordingly, the translator toolkit 20 enables asoftware application that appears the same on all platforms. The JVM canthen translate calls from the application into the appropriate systemcalls applicable to each host operating system. Importantly, the Javacode can be executed by the processor independent of the operatingsystem.

[0061]FIG. 2 illustrates in more detail the interface between anoperating system (OS) 40 and an application program (AP) 28. Theinterface, known as an application program interface 22 or API, allowsan application program 28 to communicate with the operating system 40and, thus, enables use of the operating system's functions. As will bediscussed, API 22 can either be an AWT-API or a Swing-API. If API 22 isan AWT-API, then it contains a Peer class of software components thatbridges the platform-independent software component 24 with theunderlying native graphic subsystems that are dependent on the OS 40.These graphic systems are utilized to create a visual representation,sometimes called an image, associated with the platform-independentsoftware component 24. The Peer classes within an AWT-type API 22contain mostly native methods of what will be later known as, forexample, a ButtonPeer.

[0062] If API 22 is a Swing-API, then the platform-independent component24 or Button is translated from another platform-independentimplementation within API 22, such implementation being aSwing-application, implemented as, for example, a JButtonPeer,inheriting from JComponentPeer.

[0063] Regardless of whether the API is an AWT-type or a Swing-type, aplatform-independent implementation of an object is produced and, whenexecuting that object, the object generates a visual representation 26on the display, shown in FIG. 1.

[0064]FIG. 3 illustrates the relationship between a graphical control (aButton) used in a Java application and its hardware-dependentimplementation via the AWT. Therefore, Button 30 is a subset of theobject code 32 used to generate a visual representation upon thedisplay. Button 30 is, however, code used to implement a control in aGUI environment. Such controls are describable in terms of theirgraphical attributes (i.e., their size and location on the display) andtheir characteristic behavior. For example, the graphical representationof a Button is typically a rectangular region of the display, and itsbehavior may comprise responding to a mouse click by changing its statefrom “off” to “on”, or vice-versa. Button 30 can represent an actionword on the display such that, when targeted by the pointer, theapplication program can be invoked. The dashed lines in FIG. 3 indicateinheritance. For example, the Button 30 is a type of Component 32. Thisrelationship is often described by referring to the Button as an“instance” of the “parent” Component class. Actually, since every objectin Java is an instance of a class, it is more correct to say that theButton class is descended from the Component class. The characteristicsand capabilities of the Button and Component are common across allplatforms. However, the implementation of the Button and Component willdepend on the particular machine or operating system. For example, inthe application, the programmer may have set the Background color of theButton to “gray.” If not, the actual appearance of the Button may stilldepend on the operating system, however. When the application is rununder the Windows operating system, the Button may be a light, flatgray, while on a computer running Unix®, “gray” may be rendered as abluish, metallic gray. In each case, the graphics object may bedisplayed slightly differently, due to the fact that some of the visualattributes of the object are inherited from the operating system. Inthis example, the Button does not have a graphical representation of itsown, and uses the graphical representation of the heavyweight Peer(i.e., the native Windows or Unix graphical representation of a Button).

[0065] Thus, the platform independent relationship between the Button 30and the Component 32 is mirrored in the platform-dependent AWT by theinheritance relationship between the WButtonPeer 34 and theWComponentPeer 36. As stated earlier, the heavyweight Peers associateeach of the controls in the GUI of the application program (such asButton 30) with corresponding native graphics objects in the windowingsystem of the OS. These heavyweight Peers are defined in the dynamiclinked library (dll) file, AWT.dll 38, which is specific to theoperating system 40 (e.g., Windows). As stated above, since the AWT.dllfile 38 is different for each platform, the rendering of the Button 30may vary from one operating system to another. Note that the applicationprogrammer has virtually no control over this variability.

[0066] A further consequence of reliance on the platform-dependent AWTis that a great deal of effort may be required to change or enhancefeatures in the graphical interface of a Java application, in order toensure that the change or enhancement is supported in every associatedAWT. Since the implementation of the heavyweight Peers for Java graphicscomponents is not consistent, one operating system may require littleeffort to modify, while another may be quite cumbersome.

[0067] The Swing API is an alternative to the AWT, which alleviates someof the look and feel inconsistencies that arise when portingGUI-containing Java applications to diverse operating systems. Swing ispart of the Java Foundation Classes (JFC), a set of five APIs designedto assist programmers in developing rich-featured applications. JFCcontains the AWT, Java 2D, Accessibility, Drag and Drop and Swing. Swingdoes not completely replace AWT, but extends it through the addition ofa new set of components. A subset of these components is analogous tothe basic AWT components. However, the Swing components are lightweight,as opposed to the heavyweight components of the AWT. As mentionedpreviously, lightweight components don't use platform-specificimplementations, but are instead written entirely in Java.

[0068] The relationship between a target control created by anapplication and the Swing components that render the graphicalrepresentation associated with that control is represented in FIG. 4.The target component in this example is a Swing control, JButton 48,which is derived from the Swing JComponent class 50. JComponent 50 is,in turn, a subclass of the AWT Component class 32. Because the Swingclasses JButton 48 and JComponent 50 are derived from Component class32, they inherit a Peer relationship similar to that of the heavyweightAWT controls (as represented in FIG. 3). However, in contrast to thehardware-dependent implementation of FIG. 3, the Peer 46 is lightweight,and does not reference a native graphics object from the operatingsystem. Instead, a graphical representation of the JButton 48 isdisplayed in a platform-independent manner by the JVM.

[0069]FIG. 5 illustrates the relationship between Swing, AWT and theother JFC components. The arrangement of the components in FIG. 5 isintended to represent their hierarchical status and their membershipwithin the JVM class libraries 61. The application program 60 is at thetop of the hierarchy, since it has access to all of the JFC resources.The legacy AWT 62 and the Swing API 64 are at the next level, since theyare directly invoked by the application to create and manipulate thegraphical content in its user interface. Note that the AWT 62 is notsubsumed within Swing 64, since there are some operating systemdependent features within the AWT that are not implemented in Swing. Inaddition to its GUI-related classes, Swing also relies on a collectionof support classes 66. The other API's 68 in JFC are also shown at thislevel.

[0070] Unfortunately, Swing cannot be directly employed to eliminate theplatform-dependency of the user interface in legacy applications thatuse the AWT. One reason for this is that straightforward replacement ofAWT Peers with Swing components is not possible. In Java, graphicsobjects, such as buttons, labels, sliders, etc. require a “container.” Acontainer (also referred to as a “collection”) is a component that cangroup together other components and containers. A container forms theroot component in a hierarchy of components consisting of the containerand the components within it. The top-level container in a graphicaldisplay is the Frame. Consistent with this hierarchical relationship,the components within the container are termed “children” of the“parent” container. Thus, graphics objects created by a legacyapplication program are children of the Frame in which they appear. Thearrangement of components within the Frame is referred to as the“layout,” and a Frame typically has a layout manager that controls thevisual placement of components in the Frame.

[0071] The arrangement of components in a container is comparable to astacking of layers, as illustrated in FIG. 6a. Starting with Frame 41 asthe bottommost layer, controls are added in progressive layers,overlaying the ones beneath them. If the horizontal and vertical sizeand location of the graphical controls are analogous to their X and Ycoordinates in a two-dimensional coordinate system, the counterpart ofthis stacking order is the depth, or z-axis. Hence, it is often referredto as the “z-order.” When one control overlays another, the underlyingcontrol is acting as its container. In FIG. 6a, the bottom layer is theFrame. A panel 39 is then added, by placing it on top of Frame 41. Panel39 is then overlaid by a label 37, textfield 35 and two Buttons 31 and33, noted in the examples as “OK” and “Cancel.” Thus, the panel containsthe Label, TextField and both Buttons, and is contained by the Frame. Acomposite view 29 of the Frame, with all its children, is shown in FIG.6b. Note that not all types of controls can serve as containers. Forinstance, Java does not permit stacking other objects on top of the twoButtons shown.

[0072] In the case of a legacy application program, the graphics objectsare associated with component Peers in the AWT, which invoke thegraphical resources of the operating system to render the screenrepresentation associated with each object. It would be desirable toreplace the platform-specific AWT renderings of these objects withscreen representations derived from Swing, without modifying the legacyapplication program. A simple way to accomplish this would seem to be tomerely substitute an equivalent Swing control for the originalheavyweight control. However, in order for this to work, the referenceto the original component in the application program would have to bealtered to refer to the replacement Swing control. This entailsmodifying the legacy software and the rather extensive awt.dll file eachtime a new control must be evoked, and is therefore an undesirableoption.

[0073] Another apparent solution would be to add the necessary Swingcomponents to the existing layout, allowing them to paint over theplatform-specific AWT renderings of the objects in the layout. Thiscreates difficulties for the layout manager of the Frame in which thecontrols are contained, since it results in multiple graphics objectsoccupying the same region of the Frame. Moreover, the Swing componentswould not “compete” successfully with the pre-existing heavyweightcomponents, since heavyweight components typically obscure anyoverlapping lightweight components. For example, if a lightweight Buttonwere painted over a heavyweight Button, the heavyweight Button wouldstill be visible.

[0074] Another approach would be to adapt the use of the Peer mechanism,creating lightweight Peers that, instead of invoking the graphicsresources of the operating system, instead utilize the lightweight Swingobjects. However, this tactic fails due to the fact that these Swingcomponents were not declared to be contained in the Frame by the legacyapplication. Since they are not children of the Frame, they cannotrespond to events, such as mouse clicks, directed to the correspondingregion of the screen.

[0075]FIG. 7 represents the flow of events and method calls in a legacyAWT-based application. A Frame 41 is shown at the top of FIG. 7, alongwith a complement of controls, including a Button 31. Also shown is amouse cursor 43, positioned over Button 31. In a legacy AWT-basedapplication, Frame 41 and all of its children are native objects of theoperating system. For example, if the application were running under theWindows operating system, the Button would inherit its appearance (i.e.,its shape, color, etc.) from Windows' own look and feel. The user mayclick the mouse while the cursor is positioned as shown to “push” Button31, to interact with the application program via the graphical userinterface. For example, the application program may be designed torespond to the “OK” Button being pressed by performing some calculation,displaying some result, etc. The lower half of FIG. 7 shows a functionalblock diagram representing the flow of events and method calls thatensue in an AWT-based GUI when the user presses the “OK” Button. Thedouble arrows going from left to right represent the propagation ofmethod calls, made to the native graphical objects in the windowingsystem of the operating system. The double arrows going from right toleft represent the propagation of event notification. A method call is acall or get routine to a file to invoke a graphical display, whereas anevent is a prompt to a user to interface with a displayed image, i.e., auser clicking or pushing a mouse button.

[0076] When the user clicks the mouse while the cursor is positionedover the screen image of the Button 31, that event is detected by theoperating system 40. The event notification is relayed to the awt.dllfile 38, which determines from the location of the mouse cursor that theregion of the screen devoted to Button 31 was selected when the eventoccurred. On the basis of this information, the layout manager of theFrame allows the event notification to be routed to the WButtonPeer 34,which has a pointer back to the platform independent Button 30 (theultimate target of the mouse-click event) created by the applicationprogram, causing it to change state. The application will typicallycontain code (an event handler), allowing it to respond to this changein state.

[0077] The application may call methods of the Button 30, for example,to cause it to perform some action, such as to resize or move itself.Such a method call is directed to the appropriate Peer object—in thiscase, the heavyweight WButtonPeer 34. The Peer correlates thisplatform-independent call with the necessary operating system-specificcode in the awt.dll 38 to implement the desired action. The operatingsystem 40 then performs the requested action using its native graphicsobjects and procedures.

[0078] As stated above, it would be desirable to eliminate the operatingsystem dependency of existing legacy Java applications by replacing theheavyweight implementation of the graphical objects with a lightweight,platform-independent implementation. The Swing API would appear to becapable of serving this purpose. However, as pointed out in thepreceding discussion, it is not possible to merely substitute Swing forthe heavyweight AWT API.

[0079] A system and method is disclosed that overcomes the variousdifficulties connected with migrating legacy applications from the AWTto Swing. The system and method are embodied in a functional extensionof Swing, referred to herein as AWTSwing. AWTSwing makes theplatform-independent features of Swing available to AWT-based Javaapplications. Furthermore, legacy AWT-based applications need not bemodified to use AWTSwing. AWTSwing may therefore be considered aplatform-independent version of the AWT.

[0080] The means by which AWTSwing succeeds in substituting Swingcomponents for those derived from the AWT is a further aspect of thepresent system and method. A proxy object is created that indicates tothe Swing component that it is part of the same layout as the AWT-basedcontrol. The following explanation of the manner in which this isaccomplished is set forth in FIG. 8, illustrating the relationshipbetween a Button object created by an application program and thecorresponding elements of the AWTSwing API.

[0081]FIG. 8 illustrates a Swing-type API 74 (region enclosed within thedotted lines). In FIG. 8, Button 30 is derived from the Component class32. Also, the Peer mechanism links the Button object 30 with thegraphics resources used to create and manipulate its graphic image 26,which is contained within Frame 90. However, in this case, theJButtonPeer 82 (and the JComponentPeer 84, from which it is derived) arelightweight Peers, written entirely in Java and having no dependence onthe windowing resources of the operating system. Instead, theJComponentPeer 84 intercepts key query commands related to the locationand event status of the Button object 30 and routes them to aJButtonProxy object 88. In the present embodiment, the following methodsof the Swing object are intercepted and redirected by the proxy object:

[0082] isShowing( );

[0083] getLocationOnScreen( );

[0084] getGraphics( );

[0085] proxyRequestFocus( );

[0086] requestFocus( );

[0087] getInputContext( );

[0088] getLocale( );

[0089] nextFocus( );

[0090] createImage( );

[0091] getParent( ); As a result, the JButtonProxy 88 responds to keyevents, such as focus, mouse, sizing, etc., directed to the originalAWT-based control. JButtonProxy 88 is a subclass of the Swing JComponentclass and, indirectly, of the JComponent class, and inherits methods andproperties thereof. However, Java allows for customization (commonlyreferred to as “overriding”) of inherited methods. In particular, thegetParent( ) method of the JButtonProxy identifies as its parent theFrame 90 of the target Button 30. Thus, the JButton “thinks” it belongsin the target's Frame, while the Frame knows nothing of the existence ofthe Swing component. Furthermore, when the Button 30 is asked to drawitself, the call to the drawing method of legacy AWT object isredirected by lightweight Peer 84 to JButtonProxy 88, which accesses thedrawing methods of the JButton class 48. This invokes theplatform-independent methods of Swing to paint the region of the screenoriginally allocated for the Button 30 in the AWT-based application.

[0092] The substitution of lightweight Peers, such as JButtonPeer 82,for the heavyweight Peers in the AWT, is accomplished without modifyingthe application. A utility within the JVM, known as the toolkit, createsa Peer object whenever it is necessary to display the correspondingtarget component. The toolkit may be modified so that it substitutes areference to a lightweight Peer whenever the legacy application callsfor the display of a control. Since the lightweight Peers are designedto interface to the application in exactly the same way as theheavyweight Peers, this substitution is completely transparent to theapplication.

[0093] Using the techniques described above, AWTSwing replaces most ofthe heavyweight Peers with lightweight counterparts. In the presentembodiment, the new Peer classes are arranged in the followinghierarchy:

[0094] JWindowPeer

[0095] JFileDialogPeer

[0096] JPopupMenuPeer

[0097] JMenuBarPeer

[0098] JMenuItem

[0099] JMenu

[0100] JCheckBoxMenuItem

[0101] JCanvasPeer

[0102] JPanelPeer

[0103] JScrollPanelPeer

[0104] JComponentPeer

[0105] JButtonPeer

[0106] JCheckBoxPeer

[0107] JchoicePeer

[0108] JLabelPeer

[0109] JListPeer

[0110] JTextComponentPeer

[0111] JTextAreaPeer

[0112] JTextFieldPeer

[0113] JScrollBarPeer

[0114] There is still some native code required in AWTSwing, since theSwing components JFrame, JWindow and JDialog inherit from the windowingsystem's Frame, Window and Dialog components, respectively. However,none of these components directly influences the look and feel of theuser interface.

[0115] A comparison between the heavyweight AWT API and the lightweightAWTSwing API is shown in FIG. 9. Button 30 is a graphical control usedin a legacy Java application, which employs object code 32 to generatean image 26 as part of a GUI. The user interacts with the Button 30 bypointing at, clicking on, etc. its associated image 26. The object code32 is platform independent and accesses the platform-specific graphicshardware of the computer through either of the APIs. In the case of theheavyweight API 72 the interface is provided by a heavyweight Peer 36,while in the case of the lightweight API 74 the interface is provided bya lightweight Peer 84. Both Peers are platform independent in theirinterface to the object code 32, but the heavyweight is platformspecific in its interface to the hardware and operating system of thecomputer, and the lightweight uses other platform independent interfaces(Swing) to perform its function without using the operating system.Therefore, they serve as a software translation layer between theportable Java application and its runtime environment.

[0116] In the case of the legacy AWT-type API 72, the Peer 36 makes useof a platform specific library, awt.dll 38, and the native graphicsresources of the operating system 40 to render the image 26. TheSwing-type API 74, however, uses the Proxy mechanism 88, as disclosedherein, to employ the platform-independent graphics resources of Swing86 to render the image 26. Since the lightweight Peer 84 interacts withthe object code 32 in substantially the same way as the heavyweight Peer36, the Swing-type API 74 may be substituted for the AWT-type API 72without having to modify application code or the target component code32.

[0117] By redirecting method calls intended for the original target tothe proxy, and modifying the getParent() method to return the Framecreated for the target, an environment is created in which the proxyfunctions as if it were part of the layout containing the originalheavyweight AWT control. The component is then said to be“encapsulated”. Encapsulation of the proxy component enables properevent routing and allows it to functionally replace the correspondingheavyweight control. The flow of event notifications and method calls isexplained below with reference to FIG. 10.

[0118]FIG. 10 depicts a scenario like that of FIG. 7, in which an eventis initiated by a user positioning the mouse cursor over the image of aButton on the screen and clicking the mouse button. In this case,however, we assume that the user interface associated with the Buttonbelongs to a legacy application employing AWTSwing, rather than the AWT.As explained above, Frame 41 is still a heavyweight container. The “OK”Button, however, now has no heavyweight counterpart. As a result, themouse-click event from the operating system 40 is now directed (as ageneric button-click event) to the Frame, rather than to a heavyweightButton control. The layout manager of the Frame behaves as though theFrame still contained a heavyweight Button, however, and has allocated aregion of the Frame for its graphical image. Based on the position ofthe mouse cursor at the time of the mouse-click, the Frame interpretsButton 30 as the target of the event. Therefore, the event notificationis routed by JButtonPeer 82 (which is indistinguishable to theapplication from its heavyweight counterpart), then to the JButtonProxy88. Upon receiving the mouse-click event notification, JButtonProxy 88changes state (from “off” to “on,” or vice-versa). This state changerequires that the component redraw itself (since the image of the Buttonshould now appear to be pressed), so a redraw event is propagated backfrom JButtonProxy 88 to its parent, which the proxy interprets to beFrame 41. As before, the Frame calls a lightweight method of the JButtonSwing class to redraw the image of Button 30 to indicate that it hasbeen “pressed” by the user. Proxy 88 therefore serves two purposes: totranslate method calls to appropriate Swing components within the Swinglibrary, and to translate event calls to the appropriate Frame target.

[0119] A number of significant benefits result directly from the use ofAWTSwing, for example, code maintainability is greatly improved, sincethe same API is used for all the supported operating systems.Consequently, if a problem must be corrected, or a feature added, thenecessary changes are confined to a single body of code. Thissignificantly reduces the cost of maintaining and upgrading the code.Consistent, high quality text drawing across all supported platforms isalso achieved, due to the replacement of the diverse font rasterizers inthe various operating systems by the very capable T2K/Freetype fontrasterizer. This is highly advantageous, since the text renderingcapabilities of some operating systems are quite poor. For instance, theUnix versions of the choice control, and the TextArea and TextFieldcomponents are severely limited and inconsistent with otherimplementations. Furthermore, many operating systems do not presentlysufficiently support Unicode text encoding, which can lead to problemsin preserving look and feel in international versions of software. Byimplementing the same high quality font rasterizer in all operatingsystems, many of such text-related compatibility issues would beresolved.

[0120] Therefore, it is believed that the system and method disclosedherein can be used to provide a full-featured and completely portableuser interface for Java applications, having a consistent look and feelacross all operating systems. Advantageously, it is not necessary torewrite or modify the application, but simply replace the present AWTAPI with AWTSwing.

[0121] In addition to the advantages of AWTSwing described previously,such as improved look and feel consistency and code maintainability, theuse of AWTSwing overcomes some of the problems and shortcomings inherentin the AWT. The legacy AWT implementation of listbox and choice controlsincurs substantial overhead resulting from the fact that redundantcopies are made of lists associated with these controls. This problem isrepresented in FIG. 11. When a listbox 140 or choice 142 control iscreated by an application, the application stores a list of the datarepresented in the control. Thus, at some point in the applicationprogram code the list component is declared 144, resulting in theallocation of a memory array 146 for storage of the list elements.Subsequently, when the control is displayed, the AWT inserts the listelements into the native control (Peer component) as well. This occurswhen the AWT List Peer 148 is created. Since the AWT API is heavyweight,List Peer 148 implements the target list 144 by referencing acorresponding object in the operating system 152. To do this, the ListPeer executes a copy loop 150, in which all of the items in the originalmemory array 146 are duplicated in a second array 154 accessed by theoperating system 152. This redundant memory allocation is not a seriousproblem for short lists, but can waste significant time and systemresources if the list is very long. In another embodiment of the systemand method disclosed herein, this overhead is avoided by preventing thecreation of a redundant copy of the list.

[0122] Swing is founded on an architecture in which each object in auser interface is comprised of three communicating entities: a model, aview and a controller. The model contains the underlying logicalrepresentation of the object, the view defines the visualrepresentation, and the controller specifies how to handle user input.Unlike the AWT Peer classes, the Swing listbox and choice controls usedby AWTSwing support a model that allows the list associated with thecontrol to be stored by the client of the Swing component (i.e., theapplication). FIG. 12 illustrates this use of the Swing list model. Asin the legacy case, upon creation of a listbox or choice control 144 byan application, the data represented in the control are stored in amemory array 146. When the control is displayed, a list Peer 156 iscreated; however, this time it is a lightweight AWTSwing Peer. Thislightweight Peer implements the control, not as a duplicate listobtained from the operating system, but as a lightweight Swing component160. As described above, the behavioral model for the Swing JList allowsit to refer to the original memory array 146 reserved by theapplication, rather than creating its own redundant copy of the array.

[0123] By substituting lightweight Peers for the choice and listboxcontrols, AWTSwing allows the application to utilize Swing components,rather than the heavyweight AWT components. This permits use of theSwing list model, which obviates the need for a redundant memory arrayin which to store the list elements. Furthermore, since the lightweightPeers interact with the legacy application in a manner consistent withthe original AWT Peers, no modification of the application code isrequired to obtain this benefit.

[0124] There are a number of difficulties that must be resolved in orderto create a seamless replacement for the AWT based on the Swing API.Some of these difficulties involve inherent limitations of Swing, whileothers relate to maintaining behavioral consistency with the legacy AWTcontrols. The following paragraphs examine these issues and describeembodiments of the system and method disclosed herein that address them.

[0125] Swing may impose some performance limitations when used to drawtext or labels on a display device when executing software componentshaving corresponding TextField and Label code. Poor performance in theseareas tends to be conspicuous, since the execution of TextField andLabel code are often employed in benchmark evaluations of systemperformance. The loss in performance is mainly attributable to twofactors: Swing's overhead in drawing the text, and the priority levelassigned to the text drawing operation. A further contributing factor isinitialization of undo/redo support. The priority level normallyassigned to text drawing events is not high. In fact, executing from aSwing-type API will cause most other objects to be executed before theAPI will render text on the display. As a result, the operating systemfrequently suspends text drawing temporarily to devote processor cyclesto events with higher priority. Text drawing is typically handled by adedicated procedure, known as a thread, which shares the processor'sattention concurrently with other threads. Each time the processorsuspends the text drawing thread to allow another thread to execute, itis necessary to preserve the contents of registers, memory locations,etc. containing vital text drawing information. Preserving the contentsis necessary to restore the information needed, at a later time, torender the text drawing thread upon the display. The time lost byfrequently saving and restoring the context of the text drawing threaddetracts from the performance of text drawing in Swing.

[0126] In a further embodiment of the system and method disclosedherein, a mechanism for fast text drawing is included in two of theAWTSwing lightweight Peers: JTextFieldPeer and JFastLabelPeer. Accordingto the system and method, the Swing components, JTextField and JLabel,are permitted to define the look and feel of the TextField and Label,respectively; however, they are not allowed to draw the text. Instead,when an application directs a Label object to draw itself, the eventnotification is intercepted by the AWTSwing Peer component,JFastLabelPeer. JFastLabelPeer employs its own custom code to draw thelabel, rather than the method belonging to the Swing object, JLabel.This results in much faster performance. In a similar manner, theJTextFieldPeer allows the Swing component, JTextField, to draw theborder of the TextField, but preemptively draws the text using its owncustom code. This allows the look and feel of the TextField component tobe determined by Swing, but significantly accelerates the display oftext. Once focus is given to the TextField, text drawing is handled bySwing in the customary manner. This allows the user to edit the contentof the TextField, with the full support of Swing's editing features.

[0127]FIG. 13 contains a flowchart illustrating the underlying logic forthe fast TextField and Label drawing. The flowchart reflects theconsideration given to whether a Label 120 or a TextField 122 is beingdrawn. Labels are simple objects; they display text, but have no editingcapability. TextFields, on the other hand, typically allow the user toenter or change the displayed text, and their graphical representationscontain borders surrounding the text itself, as well as selection andcursor highlighting. Thus, TextFields are more complicated objects thanLabels. While it is fairly straightforward to create an optimized textdrawing routine, replacing the Swing code that draws the entireTextField is considerably more involved. Therefore, it is preferable toallow Swing to draw the TextField border, and to provide editing andundo/redo support for the TextField, once it is created. The flowchartin FIG. 13 describes how these issues are handled by AWTSwing.

[0128] The fast text drawing logic is implemented in JTextFieldPeer andJfastLabelPeer components (see FIGS. 8 and 9), and redirects calls totext drawing methods for the TextField and Label Swing controls to usean internal fast text drawing routine. The algorithm begins bydetermining whether the text region has the focus 124 (i.e., has beenselected, using the mouse cursor). The significance of this is that theLabel or TextField can only have received the focus after it has beendisplayed on the screen. If it has not yet received the focus, a checkis made 126 to see if the region to be drawn intersects a border—inwhich case, the object being drawn must be a TextField (since Labelsdon't have borders). If not, a custom routine 128 is called to paint thebackground, and then display the text 130. If the region to be drawndoes intersect a border, the object being executed must be a TextField,rather than a Label. Drawing is therefore delegated to Swing. First, acheck is made 132 to determine whether the TextField has already beenintitialized. This refers to setting up buffers and other resourcesrequired to allow Swing to support editing the TextField. Initializationis time consuming, and is deferred until after the text is first drawnby the fast text drawing routine and editing is actually requested. Ifthe TextField has not been initialized, Swing paints the regionintersecting the border 136. Also, once the TextField has beeninitialized, Swing does all redrawing of the TextField 136.

[0129] The fast text drawing routines described above are assigned a lowevent priority by a custom event handler in the JCanvasPeer class, fromwhich both JFastLabelPeer and JTextFieldPeer are descended. The lowevent priority advantageously allows rapidly occurring changes in thetext (as might take place during a benchmark test) to be merged withtext that has previously been queued, and is waiting to be drawn. As aresult of the techniques described above, the initial display andsubsequent editing of text are both greatly accelerated.

[0130] The buffering of Swing components is another area in which theperformance of the Swing API suffers. Swing defaults to buffering itsoutput—i.e., instead of directly displaying graphics content, it isfirst drawn to an image buffer, and the entire buffer is then displayeden masse. An example of this is presented in FIG. 14. Depicted in FIG.14 is a Frame 220, containing a panel 222, which in turn contains twoButtons 224 and 226. Ordinarily, when Swing displays the Frame, it firstredraws it to a buffer in memory. When this happens, the Frame and itscontents are reconstituted as bitmaps, in a sequence based on theirz-order. In other words, a bitmap of the Frame 228 is first placed inmemory, followed by a bitmap of panel 230, and then bitmaps of theButtons 232 and 234. Finally, the composite bitmap is sent to thedisplay 236. What this means is that a bit-map of a child may displace abit-map of a parent, so that, for example, only the pixels for Buttons232 and 234 will appear in the layout area of interest on the display,and not the pixels for the underlying panel 230, where the Buttonsexist. Accordingly, the display will not present the Frame, then thepanel on top of the Frame, and then the Buttons on top of the panel.

[0131] Depending on the circumstances, buffering may result insub-optimal performance. For example, if several Swing objects arepresent within multiple levels of containment in a layout, the overheadassociated with buffering may defeat the hardware accelerationcapability of video graphics hardware within the computer. This wouldthen result in a slower-than-necessary display of the objects. On theother hand, buffering may be advantageous in a system involving remotedisplays. Rather than sending the graphic representation for each objectin the layout to a remote terminal in the sequence in which the objectsare drawn, it may be faster in such cases to draw the entire layout to alocal buffer, and then send the buffered contents in a singletransmission, thereby minimizing network traffic and bandwidth.

[0132] In yet another embodiment of the system and method disclosedherein Swing's output buffering may be dynamically enabled or disabled.AWTSwing provides access to this capability to allow the applicationprogrammer to judiciously employ buffering in situations where it willenhance graphics throughput. A modification to the Toolkit 250 withinthe JVM creates a custom attribute for instances of the JComponentPeer252, by virtue of which they are aware whether the Java applicationresponsible for their creation is operating in remote or direct mode. Inother words, the Peer knows whether the GUI images are to be presentedon a local display device, or on one that is physically remote (i.e.,accessed over a network). In the latter case, buffering is advantageous;otherwise, it is not. As mentioned above, the Swing JComponent 254 isadapted to enable or disable buffering, and this capability is inheritedby the Peer (as aJComponent subclass). JComponent 254 is the same asthat shown by reference numeral 50 in FIG. 4. Under AWTSwing, when theJComponentPeer (similar to item 84 of FIG. 8) for each of the displayedcontrols is created, buffering is automatically enabled or disabled,according to the local/remote configuration of the graphics displaysystem 256. Note that this is done without intervention by theapplication programmer, and with no modification to the applicationprogram code.

[0133] There is a further limitation of Swing that becomes a problemwhen Swing is employed to replace the AWT in legacy applications thatuse both Swing and the AWT. The look and feel settings in Swing areglobal—so, when one window changes the look and feel settings, then thechange affects all the other windows in the JVM, too. Consider the casein which a legacy application uses some of the AWT-based controls, whichinherit the look and feel of the operating system, while also usingSwing-based controls, which adopt a different look and feel based on theglobal Swing settings. If this application is migrated to AWTSwing, itmay be impossible to preserve the original look and feel, since theSwing controls that replace the original heavyweight controls of theAWT-type API will not preserve their previous look and feel. To dealwith such legacy applications, it is desirable to have the ability tomaintain more than one distinct look and feel.

[0134] The aforementioned need is addressed by allowing a unique lookand feel to be associated with a particular thread. A further feature ofAWTSwing is embodied in modifications to the UIManager, including thecreation of a thread-relative setLookAndFeel method, which only acceptscalls from a particular thread to adopt a prescribed look and feel. Thisallows individual applications to independently determine the look andfeel of the Swing components they use when the components are created.If an application doesn't invoke this method when creating an object,the object simply inherits the global look and feel (which may or maynot match the look and feel of the operating system). FIG. 16 contains ablock diagram representing a legacy mixed AWT/Swing application programand the relevant elements of the AWTSwing API that support athread-relative look and feel.

[0135] In FIG. 16, the application program 270 makes calls to both theAWT-type API 272 and the Swing-type API 276. Both APIs operate withinthe JVM 286. As previously described, the AWT calls are redirected toSwing components by AWTSwing lightweight Peers 274. The UIManager 278includes a custom method 280 for setting and resetting the look andfeel, dependent on the current thread identifier. As previouslyexplained, when application 270 needs to display a graphical control, anAWTSwing Peer 274 is created. To properly display the control, the Peerrequests the current look and feel from the UIManager, by calling astandard method 280. Based on the thread identifier of the application,the UIManager returns either the default look and feel 282 or a customlook and feel 284 associated with the application. Thus, the samecontrol created by two different threads can be rendered with distinctlook and feel characteristics. The thread-relative look and feelfunctionality of the UIManager can be enabled and disabled by theAWTSwing Peers. If a request for the current look and feel is made tothe UIManager while the thread-relative capability is disabled, thedefault settings are always returned.

[0136] The AWTSwing Peers enable the thread-relative mode when theyquery the UIManager to get the look and feel settings for a controlabout to be created, and then immediately disable it. Therefore, legacyAWT-based controls are displayed by AWTSwing API with their originallook and feel, i.e., the customer look and feel 284. However, when themixed AWT/Swing legacy application program uses Swing directly todisplay a control, no AWTSwing Peer is involved. Consequently, the Swingcontrols are always displayed with the default look and feel settings.

[0137] Another Swing-related limitation appears when Swing-based Javaapplications are ported to the OS/2 operating system, since the JVM forOS/2 does not support an OS/2 look and feel. This causes inconsistencybetween the OS/2 version of the application and versions running underother operating systems. Moreover, the look and feel of the Javaapplication is also inconsistent with that of the other applications inthe OS/2 system (which use the OS/2 windowing system). If the AWTSwingAPI is used, there are a number of options for achieving OS/2 look andfeel consistency for Java applications under the OS/2 operating system.

[0138]1. A completely new look and feel, different from that of OS/2,but consistent with an IBM corporate UI strategy, could be used. Thiswould require the creation of entirely new graphic representations forall the Swing components.

[0139]2. A complete recreation of the OS/2 look and feel could beincorporated within AWTSwing. As with the previous option, this wouldalso require entirely new graphics for all Swing components.

[0140]3. A partial OS/2 look and feel. The appearance and behavior ofAWT-based controls would be preserved, and reasonable similarity to OS/2look and feel would be provided for Swing-based controls. BecauseAWTSwing maintains behavioral compatibility with the AWT controls usedin legacy applications and has support for thread-relative look andfeel, the AWTSwing developer for an OS/2 product may choose any of theabove solutions to provide an OS/2 look and feel for Swing-basedapplications. In yet another embodiment of the system and methoddisclosed herein, the AWTSwing API supports at least one of the aboveversions of an OS/2 look and feel for the Swing components.

[0141] The behavior of certain controls in Swing is not completelyconsistent with the behavior of their AWT counterparts. Strictlyspeaking, this is not a limitation of Swing, but an issue that has to beaddressed in order to achieve the desired seamless replacement of AWT byAWTSwing. In particular, the architecture of the TextField component inAWT differs from the architecture of the JTextField and JPasswordFieldin Swing. Consequently, a creative approach to the design of theTextField Peer in AWTSwing is required to maintain the behavioralcompatibility of TextField controls, as required for the support oflegacy applications. In yet another embodiment of the system and methoddisclosed herein, AWTSwing provides mode-switching capability in theTextField component. The manner in which this is achieved is describedbelow.

[0142] In AWT, the TextField component can be used as both a normal textfield and a password-protected field. If an echo character is specifiedfor the text field, the characters of a user-entered password will notbe displayed as they are keyed in, but will instead be overwritten bythe echo character. This prevents someone else from easily learning thepassword by surreptitiously observing the user enter it. In Swing, thenormal and password-protected behaviors are not shared by a singlecomponent, but separately allocated to the JTextField and JPasswordFieldcomponents. To emulate the TextField in the AWT, however, thesecomponents must be deployed differently from the other lightweight Swingcomponents. This is represented in FIG. 17.

[0143] Normally, Swing components are created only during theconstruction of the Peer object. However, in order to reproduce thebehavior of the legacy AWT-based TextField control 170, JTextFieldPeer172 must dynamically switch between the two Swing objects when the modeof use changes. This is accomplished by creating a new JTextFieldProxy174 or JPasswordTextFieldProxy 176 object, depending on the settings ofthe echo character, and transferring the properties from the old to thenew component. The appropriate Swing component is in effect “switchedin” as a functional replacement for the AWT TextField, according to itsmode of use. For example, if a legacy application is using a TextFieldwithout password protection, no echo character is set. In this case, theJTextFieldPeer uses the Swing TextField component. Now, if the legacyapplication activates password protection, the AWT TextField will beassigned an echo character. When this occurs, the JTextFieldPeer createsan instance of Swing's JPasswordField component and substitutes it forthe original AWT TextField control. This is done dynamically, so thateach time the application changes the echo character status, theappropriate Swing replacement object (JTextField or JPasswordTextField)is created and used to replace the previous replacement object. Thus,the mode-switching capability of AWTSwing permits two Swing componentsto alternate as replacements for an AWT TextField component, dependingon the manner in which the TextField is being used by the application.

[0144] A flowchart representing the logic for dynamic TextField modeswitching is presented in FIG. 18. Upon entry 192, the algorithm tests178 the status of the echo character. If has been no change in the stateof the echo character, then whichever Swing control is in use (eitherJTextField or JPasswordField) is retained, and nothing needs to be done190. On the other hand, if the echo status has changed, then it isnecessary to swap the JTextField Swing component for a JPasswordField,or vice-versa. Before making this switch, the state (color, position,text, etc) of the control that is presently being displayed is saved180. Once this information is captured, the current object can bedestroyed 182, and its alternate created 184. After it is initialized186, the previously saved state is applied to the new component, and theprocedure is finished 190.

[0145] AWTSwing employs a different color inheritance behavior than thatemployed by the AWT. This change is necessary, in order to maintaincompatibility with legacy AWT-based applications and still allow Swingto set the look and feel of the user interface. For AWT-based Javaapplications, if the background color for a control is not explicitlyset, it is inherited from the control's parent. For example, a Buttonappearing on a panel will automatically be assigned the same backgroundcolor as the panel, unless the Button color has been expressly declared.The color inheritance scheme for AWT is illustrated in FIG. 19a. FIG.19a depicts a Frame 200 containing a Label 202. The Frame has abackground color assignment 204. If the background color is notexplicitly defined (i.e. color setting=NULL), the Label 202 inherits itsbackground color from its parent (i.e., the Frame 200).

[0146] In contrast to this practice, it is normal for controls inSwing-based Java applications to receive their background colorassignment from Swing (if it is not explicitly declared). Consequently,when upgrading from AWT to AWTSwing, the color inheritance mechanismmust be modified to allow the background and foreground color ofcontrols to be set by Swing, while also preserving the capability forcontrols to inherit this setting from their parent in legacyapplications.

[0147] In yet another embodiment of the system and method disclosedherein, this is accomplished by adopting the following color inheritanceorder:

[0148]1. If the background color for the control is explicitly declared,AWTSwing uses this setting to display the control.

[0149]2. If the background color for the control is not explicitlydeclared, and AWTSwing attempts to get the color from the Swingsettings.

[0150]3. If the background color for the control is not explicitlydeclared, and is not available from Swing settings, AWTSwing displaysthe control using the background color of the control's parent. Thisinheritance scheme allows normal inheritance of background color fromglobal look and feel settings in Swing. However, it defaults to the AWTscheme of inheritance from the parent when these global settings areunavailable. An explicit declaration of the control's background coloroverrides either type of inheritance. Furthermore, this colorinheritance mechanism offers considerable flexibility in displayingcomponents created by legacy applications. When a control must inheritits background color from its parent, either the parent of the originalAWT-based object, or that of its Swing counterpart can be used. Thisoption is made possible by the replacement of AWT-based heavyweightPeers by AWTSwing proxy components, discussed earlier. A diagramrepresenting the new color inheritance scheme appears in FIG. 19b.

[0151]FIG. 19b shows a Frame 200 and Button 202, with their respectivecolor properties 204 and 206. In this case, if the method call to getthe background color setting 206 of the Button 202 returns a NULL, it isdirected by the JButtonPeer 208 to the JButtonProxy 210. SinceJButtonProxy is a Swing component, its color setting is inherited fromthe Swing JButton class 212, of which it is a subclass. If thebackground color setting 214 for Swing is also undefined, JButtonProxyreturns the background color 204 of the Button's parent (i.e., the Frame200).

[0152] Providing this new color inheritance mechanism in AWTSwingrequires the creation of a new method, which can be invoked to returnthe background color declaration (if any) of a given component, theSwing settings for the background color of the component, or thebackground color of the component's parent. The standard SwinggetBackground method is insufficient for this purpose, since itautomatically returns the background color of the component's parentwhen there is no explicit declaration for the component.

[0153] In addition to resolving problems such as those described above,the system and method disclosed herein provide enhanced graphicsfunctionality, exceeding that of many targeted operating systems. In yetanother embodiment of the system and method disclosed herein, anenhanced feature set, consisting of features from operating systems withsophisticated GUIs may be incorporated into AWTSwing. This enhancedfeature set would then be available to Java applications running underthe operating system into which AWTSwing is installed. For example, theGUI built into the Windows operating system allows the use of pop-upmenus, with editing and undo/redo support. This is a very helpfulfeature for a user interface, but is not available in the Unix operatingsystem. However, a programmer could include pop-up menus in the userinterface for his application, and port the application to a Unix systemusing AWTSwing, where the pop-up menus would be displayed exactly asthey appear on the Windows-based computer in his office.

[0154] The Accessibility Bridge is another built-in feature of theWindows operating system, which allows a visually handicapped user toselectively magnify portions of the computer screen to improvevisibility. AWTSwing makes this capability available as an enhancementto legacy AWT-based programs, not just Swing programs, and it does sowithout requiring a change in the application. Accessibility featuresavailable in Swing become generally available to legacy AWTapplications.

[0155] The comprehensive feature set of AWTSwing is available to anapplication program, despite limitations in the graphics resources ofthe operating system under which the program executes. For example,Motif is a GUT guideline and development toolkit for the X WindowSystem. As such, Motif defines the standard GUI look and feel for mostUNIX-based operating systems and their applications. Although thequality of the choice control (a type of ListBox) in Motif is poor, aJava application supported by AWTSwing in Unix renders a much higherquality choice control, consistent with the more attractive look andfeel of an operating system like Windows.

[0156] The processing and display of text is a major area ofinconsistency between different operating systems. As mentioned earlier,Unicode text encoding is not supported in many operating systems. Thisis a significant disadvantage when trying to maintain a consistent lookand feel in software with international versions, requiring foreigncharacter sets and complete simultaneous coverage of internationalcharacter sets. In legacy AWT-based systems, characters are converted tolocalized encodings before the text is rasterized. This can result ininconsistent or inaccurate text renderings. Moreover, the AWT-based textcontrols are capable of using only one font at a time. Therefore,complex strings, containing characters from two or more fonts, willoften be incorrectly rendered.

[0157] A further capability of AWTSwing, not present in some operatingsystems, is font searching. In order to display text, the operatingsystem must rasterize the characters used in the text. This involvesassociating with each character an arrangement of graphic shapes (calledglyphs) with the character, that constitute its screen representation.For example, the glyph for the letter “H” is composed of two verticalstrokes joined by a horizontal stroke. Note that various glyphs may bechosen to rasterize a character, depending on the style and typeface ofthe text. For instance, a different set of glyphs would be used torepresent text in a bold Courier typeface than in italicized Garamond.When font searching is enabled, an operating system searches a set offonts for the necessary characters. This enables complex strings,containing characters from two or more fonts, to be drawn correctly.Advantageously, AWTSwing provides this enhanced capability independentlyof the operating system, because all text drawing is through Java anddoes not utilize the platform-specific controls.

[0158] It will be appreciated by those skilled in the art having thebenefit of this disclosure that this invention is believed to present anAPI for the creation of a platform independent GUI for Javaapplications, and which can replace the heavyweight API used by legacyapplications without having to modify the application. Furthermodifications and alternative embodiments of various aspects of theinvention will be apparent to those skilled in the art in view of thisdescription. Such details as the exact composition of the enhancedfeature set, or the number of AWTSwing Peer classes as described hereinare exemplary of a particular embodiment. It is intended that thefollowing claims be interpreted to embrace all such modifications andchanges and, accordingly, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense.

What is claimed is:
 1. A display system, comprising: a display; anapplication program adapted to execute from a processor that alsooperates from an operating system; a memory; a software componentcontaining lines of code which, during execution of the applicationprogram, fetch a list of text contained within the memory for producingan image of the list upon the display absent invoking a display routinefrom the operating system.
 2. The display system as recited in claim 1,wherein the application program is adapted to operate during runtime ofthe operating system, wherein the application program creates the listprior to fetching the list from the memory.
 3. The display system asrecited in claim 1, wherein the list is created only once in the memoryby the application program, and not again by the operating system. 4.The display system as recited in claim 1, wherein the image of the listupon the display is created independent of the operating system.
 5. Thedisplay system as recited in claim 1, further comprising a peercomponent coupled between the software component and a list of Javaswing component, said peer component containing a pointer fortranslating call routines from the software component to the memorycontaining the list of text.
 6. The display system as recited in claim5, wherein the lines of code within the software component comprise anobject which, when presented on the display, produces a graphicalrepresentation, and wherein the peer component emulates at least some ofthe behavior of a second peer component adapted to serve as an interfacebetween the software component and the object such that the second peercomponent creates a copy of the list.
 7. The display system as recitedin claim 6, wherein the second peer component is part of the abstractwindowing toolkit (AWT).
 8. The display system as recited in claim 6,wherein the system of software components comprises a Java swingapplication program interface (API).
 9. The display system as recited inclaim 6, wherein the object is part of a graphical user interfaceassociated with the application program.
 10. The display system asrecited in claim 6, wherein the object is a choice or list control. 11.The display system as recited in claim 1, wherein the applicationprogram is written in Java programming language.
 12. A method fordisplaying an image, comprising: running an application program upon acomputer operating under an operating system also running on thecomputer; and creating a list file during said running of theapplication program by pointing a call routine created in theapplication program to a library of platform-independent commands andstoring the created list file in memory without creating a copy of thelist file in memory.
 13. The method as recited in claim 12, wherein saidcreating comprises communicating the call routine to lines of codewithin a peer software component that serves as an interface betweenobject code created while running the application program and an imageformed on a display.
 14. The method as recited in claim 12, wherein saidcreating comprises communicating the call routine to lines of codewithin a peer software component that serves to point to the list filewithin the memory.
 15. The method as recited in claim 13, furthercomprising emulating, via the peer component, at least some of thebehavior of a second peer component serving as an interface between theobject code and its corresponding image.
 16. The method as recited inclaim 13, wherein the object code is part of a graphical user interfaceassociated with the application program.
 17. A computer-readable storagedevice, comprising: a single copy of a code listing that, when executedby a processor, produces an image containing a list of items which canbe selected by a user via a pointing device; an operating system foroperating a computer that includes the storage device; and anapplication program adapted to create the code listing absent anyinvolvement of the operating system by sending call instructions to asoftware component that draws from commands within a library that areindependent of said operating system, and importing said commands assaid lines of code listing.